The present invention relates to a semiconductor light-emitting device arranged on an insulating substrate, and particularly to a semiconductor light-emitting device consisting essentially of gallium nitride compound semiconductors formed on a sapphire substrate.
In recent years, attention has been paid to gallium nitride-based compound semiconductors, such as GaN, as materials of short-wavelength light emitting diodes (LED) or semiconductor laser devices (LD) for use in a range between blue light and ultraviolet. It is expected that a blue light semiconductor laser device using such a material will be applied to a light source for high-density information processing, because of its short oscillation wavelength.
Conventionally, gallium nitride-based compound semiconductor layers are grown and stacked on a sapphire substrate. Where an electrical contact is formed on a layer close to the substrate, among the stacked layers on the substrate, it is necessary to etch and remove part of the surface-side layers, since sapphire is insulating. In a device, such as a light-emitting diode, in which the whole light-emitting intensity is important, the above-described etching process should be considered, because it decreases the light-emitting area of the device, thereby directly lowering the light-emitting intensity.
As shown in Jpn. Pat. Appln. KOKAI Publication No. 6-338632, it has been proposed to arrange a pair of electrodes on diagonally opposite sides in order to increase the light-emitting area. However, this publication only shows a relationship between the position of the electrodes and effective flow of electric current, and does not refer to a method of increasing the light-emitting area or decreasing the electrode area. From the point of view of increasing the light-emitting area itself, it is preferable to lead an electrode out through a hole formed in a top surface, as shown in Jpn. Pat. Appln. KOKAI Publication No. 4-273175. In this proposal, however, since the light-emitting area is shielded by an expanded electrode when viewed from the top, the light-emitting area is substantially not increased.
As described above, a light-emitting device of compound semiconductors arranged on an insulating substrate needs to have a pair of electrodes arranged on its light-output face. Since the electrodes need to be connected to bonding wires, and thus should not be so small, the electrodes cause a decrease in the light-emitting area.
An object of the present invention is to increase the light-emitting area of a light-output face, and to firmly connect electrode pads to outer leads, in a semiconductor light-emitting device arranged on an insulating substrate.
According to a first aspect of the present invention, there is provided a semiconductor light-emitting device having a light-output face facing in a first direction, comprising:
a multi-layer structure defining the light-output face and having a plurality of semiconductor layers stacked in the first direction to form a pn junction for emitting light, the semiconductor layers including a first and second semiconductor layers of first and second conductivity types, respectively, interposing the pn junction;
a first main electrode arranged on the first semiconductor layer, and having a first electrode pad which covers the light-output face and does not transmit an emitted light;
a second main electrode arranged on the second semiconductor layer, and having a second electrode pad which covers the light-output face and does not transmit an emitted light, the first and second electrode pads having a total projected area set at 25% or less of that of the light-output face;
first and second insulating layers arranged on side walls of the multi-layer structure; and
first and second wiring layers arranged on the first and second insulating layers, respectively, and connected to the first and second electrode pads, respectively.
According to a second aspect of the present invention, there is provided a semiconductor laser device comprising:
a support substrate consisting essentially of sapphire;
a multi-layer structure having a plurality of gallium nitride-based compound semiconductor layers stacked on the support substrate to form a laser cavity, the semiconductor layers including an active layer and n-type and p-type semiconductor layers interposing the active layer, the n-type semiconductor layer being closer to the support substrate;
a lead-out groove formed in the multi-layer structure to extend in parallel to the laser cavity and have a depth from the p-type semiconductor layer to the n-type semiconductor layer;
a first main electrode arranged in contact with the n-type semiconductor layer at the bottom of the groove; and
a second main electrode arranged in contact with the p-type semiconductor layer,
wherein the first and second main electrode have first and second electrode pads, respectively, which are arranged on substantially the same plane to interpose the lead-out groove.
According to a third aspect of the present invention, there is provided a semiconductor laser device comprising:
an insulating support substrate;
a multi-layer structure having a plurality of Group III nitride semiconductor layers stacked on the support substrate to form a laser cavity, the semiconductor layers including an active layer and first and second semiconductor layers of first and second conductivity types, respectively, interposing the active layer;
first and second main electrodes arranged on the first and second semiconductor layers, respectively, and having first and second electrode pads, respectively;
an insulating layer arranged on a side wall of the multi-layer structure;
a mount frame supporting the multi-layer structure through the support substrate and having a pair of mount electrode pads used as n-side and p-side electrodes, respectively;
a first wiring layer arranged on or above the insulating layer and electrically connecting the first electrode pad and one of the pair of mount electrode pads, the first wiring layer having a thickness larger than that of the first electrode pad to function as a heat-discharging member for discharging heat generated in the multi-layer structure; and
a second wiring layer electrically connecting the second electrode pad and the other of the pair of mount electrode pads.
According to the present invention, electrode pads on a light-output face are decreased in area to increase a light-emitting area, so that a light-emitting device with high brightness is realized. Where the electrode pads of a chip and the electrode pads of a mount frame are connected by solder or facedown, not by means of wire bonding, the connection is ensured even when the electrode pads are small. As a result, a device, which has a semiconductor multi-layer structure arranged on an insulating substrate, can have an increased light-emitting area on its light-output face and reliable wiring connection to its electrode pads. Where the electrode pads of a chip and the electrode pads of a mount frame are electrically connected through thick wiring layers formed by coating, the heat-discharging characteristic of the device can be improved.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out in the appended claims.